Increases in the cost of petroleum and concerns about future shortages has led to increased interest in other carbonaceous energy resources, such as biomass for the production of useful fuel and chemical products. Biomass is an important component of a comprehensive energy strategy for use of domestic resources to insure energy independence and to simultaneously reduce the overall GHG footprint of associated processes. Various processes have been proposed for converting such materials to liquid and gaseous fuel products including gasoline, diesel fuel, aviation fuel and heating oils, and, in some cases, to other products such as lubricants, chemicals and synthetic fertilizers.
A number of problems that have hampered widespread use of these routes include the relatively low thermal efficiency of conventional technologies and the inability to use various process by-products such as CO2, char and waste inorganics for beneficial effects. The conversion of all or selected portions of the biomass, which has a hydrogen to carbon (H/C) ratio of approximately 1:1 up to about 2:1, to hydrocarbon products, such as fuels that have H/C ratio of something greater than 2:1, results in up to half of the carbon in the biomass being converted to CO2 and vented to the atmosphere, and thereby wasted. Additionally, the fact that, heretofore, a large amount of greenhouse gas (GHG), particularly in the form of CO2, is emitted to the atmosphere as a waste product in the conversion of biomass to useful products has caused biomass to liquids (BTL) processes to be questioned by many from an environmental point of view.
It has been proposed to at least partially overcome the GHG problem by capturing and sequestering the carbon dioxide by re-injecting it into subterranean formations. Such an arrangement has the disadvantages of being expensive, of further reducing the process energy efficiency, of requiring the availability of appropriate subterranean formations somewhere in the vicinity of the conversion facility, of concerns about the subsequent escape into the atmosphere of the carbon dioxide, and the waste of the energy potential of the carbon content of the carbon dioxide.
Direct pyrolysis methods have been developed for liquefying carbonaceous materials such as biomass, but these too generate unwanted byproducts such as char and inorganics that are of limited or no value. Moreover, none of these proposed arrangements achieve the combination of thermal efficiency, low cost and substantially reduced GHG emissions that would be required for them to be economically and environmentally attractive. There remains an important need for economical biomass to liquids conversion processes with reduced carbon dioxide emissions coupled with the efficient use of the CO2, carbon and inorganic byproducts.